At the bottom of the networking food chain, so to speak, are hubs. Hubs are used in networks that use twisted-pair cabling to connect devices. Hubs can also be joined together to create larger networks. Hubs are simple devices that direct data packets to all devices connected to the hub, regardless of whether the data package is destined for the device. This makes them inefficient devices and can create a performance bottleneck on busy networks.
In their most basic form, a hub does nothing except provide a pathway for the electrical signals to travel along. Such a device is called a passive hub. Far more common nowadays is an active hub, which as well as providing a path for the data signals, regenerates the signal before it forwards it to all of the connected devices. A hub does not perform any processing on the data that it forwards, nor does it perform any error checking.
Hubs come in a variety of shapes and sizes. Small hubs with five or eight connection ports are commonly referred to as workgroup hubs. Others can accommodate larger numbers of devices (normally up to 32). These are referred to as high-density devices. Because hubs don't perform any processing, they do little except enable communication between connected devices. For today's high-demand network applications, something with a little more intelligence is required. That's where switches come in.